content: /**
   * Copyright (c) 2016-present, RxJava Contributors.
   *
   * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
   * compliance with the License. You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software distributed under the License is
   * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
   * the License for the specific language governing permissions and limitations under the License.
   */
  
  package io.reactivex.observable;
  
  import io.reactivex.common.annotations.NonNull;
  
  /**
   * Convenience interface and callback used by the compose operator to turn a Completable into another
   * Completable fluently.
   */
  public interface CompletableTransformer {
      /**
       * Applies a function to the upstream Completable and returns a CompletableSource.
       * @param upstream the upstream Completable instance
       * @return the transformed CompletableSource instance
       */
      @NonNull
      CompletableSource apply(@NonNull Completable upstream);
  }
  